1. Velocity Profiles. The dimensionless velocity profiles at the downstream Station B-4 are compared i n Figures 8a through 8c for Mach 0.5, both with and without ISJ noise. For the reference f l a t plate, it i s seen that acoustic disturbances did not discerni b l y affect the development o f the turbulent boundary later for noise levels typical of an engine fan exit duct as studied here; with the possible exception of an increase i n the magnitude i n the wake component. This i s i n agreement with observations by Benet 6. However, sound pressure level has some effect on the boundary layer of the acoustic specimens, as can be seen i n Figures 8b and 8c. S'imilar behavior has been observed at Mach 0.3 and 0.7, Stations 8-2 and 8-3, and the 60-Ray 1 woven 1 composite specimen.
2. Momentum Thickness. The momentum thickness (in feet) as a tunction of the distance (in feet) from Station 0-1 i s shown i n Figures 9(a) through 9(e) for a l l the specimens, including the reference f l a t plate. One might attempt t o infer the skin-friction coefficient by differentiating the measured momentum thickness, 0 , with respect t o the distance, X, as the Pohlhausen integral method. would indicate'. However, the resulting skin-friction coefficient inferred from this would involve serious error, as differentiating i n such a small distance i s a divergent operation.
3. Skin friction on a flat perforated acoustic liner